Phil Plait asked me about this and I took one look at it and said "cosmic ray hit." Here's the picture, right Navcam from sol 589:If you compare the image to the left eye taken at exactly the same moment, there is no bright pixel -- this is diagnostic of an event that affected only one camera, so is most likely a cosmic ray hit:Another thing that tells you it's likely a cosmic ray hit and not a bleeding pixel from something bright is the fact that pixel bleeding on Navcams happens in the horizontal, not vertical direction. Just check any Navcam image of the Sun, or this low-light image from sol 593 in which the sloping side of the RTG is overexposed and bleeding horizontally. By contrast, cosmic ray hits can be oriented in any direction, such as in this nighttime Navcam pic.

And I figured my debunking work was done, until someone pointed out to me that there's another right Navcam image, shot from a similar but not identical location, at the same time of day, pointed in roughly the same direction, that also contains a bright dot. Here's the picture, right Navcam from sol 588:As with the sol 589 image, the bright dot is not in the Left Navcam frame taken simultaneously, although this time that fact is explained by the presence of a foreground butte blocking the field of view:

This dot is different from the other one. It is not extended vertically. It's just a dot, that overlaps more than one pixel. Still, I would be inclined to dismiss this as a cosmic ray hit (saturating pixels, in one eye and not the other) without extraordinary evidence to the contrary. There are interesting coincidences here that could lend themselves to an alternative explanation, such as a specular reflection from a bright object: both are on the horizon, seen in the same direction, at the same time of day. But there is another coincidence that has me skeptical: seen in right eye only of the Navcam. And the vertical extension of the bright pixel in the sol 589 image just doesn't make sense for a specular glint; that would extend horizontally, not vertically, while cosmic ray hits can make streaks in any direction. So I am still inclined toward cosmic ray hits and coincidence, but I'll admit to being less totally certain about that after seeing the sol 588 image than I was after seeing the sol 589 image alone. And now there's this from engineering camera lead Justin Maki, via Alan Boyle:

QUOTE

"Bright spots appear in single images taken by the Navigation Camera on NASA's Curiosity Mars rover on April 2 and April 3. Each is in an image taken by this stereo camera's right-eye camera [with links to the April 3 and April 2 pictures] but not in images taken within a second of each of those by the left-eye camera [again, with links to April 3 and April 2]. In the two right-eye images, the spot is in different locations of the image frame and, in both cases, at the ground surface level in front of a crater rim on the horizon.

"One possibility is that the light is the glint from a rock surface reflecting the sun. When these images were taken each day, the sun was in the same direction as the bright spot, west-northwest from the rover, and relatively low in the sky. The rover science team is also looking at the possibility that the bright spots could be sunlight reaching the camera's CCD directly through a vent hole in the camera housing, which has happened previously on other cameras on Curiosity and other Mars rovers when the geometry of the incoming sunlight relative to the camera is precisely aligned.

"We think it's either a vent-hole light leak or a glinty rock."

Anybody got anything else to add? Other images of this spot? Where is the spot on the map, exactly? I can (and have) drawn lines on Joe Knapp's map but I'm not convinced I understand the geometry precisely enough to want to say anything about where any putative reflective object would be.

Only thing I have to add: Many people here will remember, earlier in the mission, we had a whole discussion of sparkles that (I'm going to say now) probably were glints off rocks - because it seems like there were too many to be readily explained by bits of hardware laying around, and also we've seen a lot of polished, shiny rocks. I can't find the discussion at the moment. All of those glints appeared in both cameras, though (which is why we thought they might actually be interesting).

I noticed the 588 blip at the time since it appears to sit on the distant ridge and doesn't obviously look like a cosmic ray hit (unlike the 589 blip, as you point out Emily). The lack of lnav to confirm it as a cosmic ray at first disappointed me. But then I remembered that (MSL especially) overlaps the navcams considerably. So the neighbouring rnav shows the same region as the 588 blip:http://mars.jpl.nasa.gov/msl-raw-images/pr...NCAM00252M_.JPGNo surprise: no blip. My conclusion at the time: cosmic ray. I see nothing new here to change my mind.

My very crude take on triangulation from the two Navcam images - put me in a spot that I think is also visible in one of the Sol 580 MastCam mosaics.... perhaps the tall thin rock left of center, near the top, on that rock face, is the cause of the excitement.

Here's another "glint" from the right navcam, on sol 589. Also in the top left corner of the image, somewhat on the apparent horizon. Note the camera is pointing in completely different direction. Left camera shows no glint.

How simultaneously are the navcam pairs taken? If there is even a small delay then one camera might miss a very small glint that was 'twinkling'. That seems unlikely but I can't think of any other way a real feature in the landscape could be missed by the other camera. It's surely too distant for the difference in viewing angle to come into play.

Well - we have one pair where the feature is clearly hidden behind a nearby hill. The other pair is more curious - it may very well be the exact same situation - more local topography occluding it in one eye. I believe it's near instantaneous - the have the same spacecraft clock time time to the second.

Depending on the smoothness of the surface, specular reflection is heavily dependent on the angle between the pixel and the surface normal of the object it's viewing. If the light reflected off the surface almost perfectly aligns with the camera, you will see the glint, otherwise you won't, even with a very small change in viewing angle between the two cameras.

It could be that one camera pixel or pixels is very closely aligned with the reflection angle, whereas the other camera is off slightly and little of the specular reflection travels to it comparatively. I'm not convinced that's it, as over several km the difference in viewing angle will be very small and would require a very very smooth surface. I'm not sure about the pixel bleeding that Emily is talking about either, I'll have to look into that. Just something to think about though.

I was absolutely 100% "It's a CR hit" when I saw them. I've done a complete 180. 589 could be a CR hit. 588 isn't. It hides behind a hill behind the two eyes. It also happens to triangulate well with the Sol 580 MastCam and 589 Navcam feature to a tall, thin shiny rock.

Huh? Do you mean that it's visible in 588 rnav but not 588 lnav? That's also consistent with a cosmic ray hit on the rnav and not the lnav! It's certainly not evidence that 588 is not a CR hit. And the fact that the other 588 rnav frame shows absolutely nothing also points to a CR.

The Sol 588 observation ( visible in Right, not in Left ) is entirely consistent with an actual object being obscured by the perspective shift between the two eyes applied to the northern side of the nearby topography.

The Sol 589 observation does not have a similar topography to explain it's one-eye appearance (although a small rock on the nearby topography might explain it )

However, if one triangulates between the two observations, one finds a point on a small ridge line. That point is also visible in Sol 580 MastCam imagery that shows a tall, thing, bright rock at the exact same point ( see my first post on this thread )

This means either....

1) 2 CR hits happened to appear on two images on the same camera on two sols at different pixel locations that happens to be geometrically consistent with a tall thin bright rock see 8 sols earlier ( which is QUITE a coincidence )

2) It's an actual thing.

I'd expect M100/M35 and ChemCam imagery of the same spot to be acquired soon that should quite easily settle the matter. The object, if it's real, is approx 160 meters away.

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